The present invention relates to air circulation devices and, more particularly, air circulation devices of the squirrel cage type. Centrifugal fans or blowers, also commonly referred to as squirrel cage blowers, are ubiquitous. They are used in such things as home appliances, office equipment, and automobile heater/AC units. The operating principal is the same for all centrifugal blowers. The air is drawn in at the inlet by a rotating impeller which is driven by a motor and contains a number of blower blades spaced apart and arranged in a circular pattern. On flowing through passages between the blower blades, the air is given an acceleration and emerges at an outlet under pressure from the blower housing.
Although such blowers have many desirable features, they suffer from several common problems. Air often flows around the end of the impeller and back into air inlet of the blower and onto the blower blades. Because there is little or nor seal to prevent air from flowing back into the blower, significant amounts of air recirculates into the blower's air inlet, which in turn causes chaotic air flow at the inlet side of the blades. Consequently, there is an inordinate amount of vibration and noise created because the air cannot flow onto the blower blades in a smooth and orderly manner. Thus, there is a need in the art for an improved blower of the squirrel cage type that effectively reduces or eliminates the back flow and recirculation of air into the air inlet.
Prior art squirrel cage blowers are also often characterized by highly forward curved blower blades that have nearly radial entry angles (see FIG. 5). This is particularly problematic and can cause air flow instability when the blower is attached to a volume with a restricted outlet area. The restricted flow outlet and the forward curved blower blades can generate a negative damping that causes a Helmholtz resonator-type of oscillation to occur in the system and produce unwanted noise. As such, there is also a need in the art for improved blower blade design that reduces unwanted noise and vibration and improves the efficiency of the blower.
It can therefore be seen that there is a real and continuing need for the development of an improved squirrel cage type blower that reduces noise and vibration and improves efficiency.
The primary objective of the present invention is the provision of an improved squirrel cage type blower that reduces or eliminates the back flow or recirculation of air through the air inlet.
Another objective of the present invention is the provision of an improved squirrel cage type blower that minimizes the vibration and noise and improves efficiency through a more effective blower blade design.
Another objective of the present invention is the provision of a method of reducing the noise and vibration and improving the efficiency of a squirrel cage type blower.
Still another objective of the present invention is the provision of an improved squirrel cage type blower that is efficient in operation, economical to manufacture, and durable in use.
These and other features, objectives, and advantages will become apparent to those skilled in the art with reference to the accompanying specification.